Differential with lubrication ports

ABSTRACT

Systems for a differential are provided. The differential includes two sets of pinion gears with an asymmetric split tooth profile. A case of the differential includes a plurality of lubrication ports which open adjacent to untoothed sections of one set of pinion gears and in a drive mode and an outboard axial load is exerted on the corresponding set of pinion gears.

TECHNICAL FIELD

The present description relates generally to a differential in avehicle. More particularly, the present disclosure relates to adifferential with lubricant distribution features.

BACKGROUND & SUMMARY

Vehicle differentials, such as open differentials, permit speeddifferentiation between axle shafts which deliver power to drive wheels.Wheel slip during vehicle cornering is avoided when speeddifferentiation between the axle shafts is permitted. However, in lowtraction environments, the open differential permits the drive wheelwith a lower friction coefficient to rotate at a higher speed than theopposing wheel, resulting in wheel slip.

A desire to increase vehicle traction led to the development of limitedslip differentials. This limited slip functionality allows the deviationbetween axle shaft speeds to be constrained to reduce the chance ofwheel slip. To alter handling performance under variable tractionconditions, these limited slip differentials may transfer a greateramount of torque to the drive wheel with less traction. One examplelimited slip differential is shown by Yamazaki et al. in U.S. Pat. No.7,029,415 B2. Yamazaki teaches a differential with a case and aplurality of pinion gears that mesh with a pair of side gears. Yamazakifurther provides a lubricant hole in the case in an attempt to directoil to the gears housed therein.

The inventors herein have recognized potential issues with Yamazaki'slimited slip differential and other differential systems. As oneexample, the pinion gears disclosed by Yamazaki may exhibit unbalancedgear meshing due to the asymmetric tooth arrangement of the gears,leading to uneven wear amongst the gears. Further, the singlelubrication hole in Yamazaki's differential may not achieve balancedlubricant distribution within a differential case and may be unable toflow desired amounts of lubricant to targeted regions that experiencehigher loads, for example. The potential for uneven wear of thedifferential components is consequently increased, thereby decreasingthe differential's lifespan.

To overcome at least some of the aforementioned challenges, adifferential is provided. In one example, the differential comprises twosets of pinion gears. Each of the gears in each set of pinions includesan untoothed section positioned between a wider toothed section and anarrower toothed section. The differential further includes a first sidegear that meshes with the wider toothed sections of the first set ofpinion gears. Still further, the differential includes a second sidegear that meshes with the wider toothed sections of the second set ofpinion gears. The differential further includes a case that comprises alubrication port. The lubrication port opens radially adjacent to one ofthe pinion gears in the first set of pinion gears. In this example,during a drive state, an axial load on the first side gear is in aninboard direction. In this way, the position of the lubrication port inthe case of the differential allows lubricant to be delivered to atargeted region of the differential which may experience higher loads,thereby decreasing wear on the gearing system and increasingdifferential longevity.

As one example, the differential case may include a plurality oflubrication ports. In this example, each lubrication port opens radiallyadjacent to a separate pinion gear in a first set of pinion gears. Inthis way, the lubrication ports provide more balanced lubricantdistribution. Consequently, the potential for uneven wear on the gearingsystem is decreased which may further increase differential longevity.

As another example, the differential case may comprise a continuous(e.g., monolithic) structure, which may increase the overall strengthand reliability of the differential. Further, structuring the case inthis manner reduces the overall number of parts of the differential. Thedifferential's manufacturing duration may be decreased, as a result.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a vehicle powertrain with adifferential.

FIG. 2 is an exploded view of a differential according to an example ofthe present disclosure.

FIG. 3 is a perspective view of the differential, depicted in FIG. 2, inan assembled state.

FIGS. 4A-4B are cross-sectional views of the differential, depicted inFIG. 3.

FIG. 5 is a cross-sectional view of the differential, depicted in FIG.3.

FIGS. 6A-6B are detailed views a pinion gear included in thedifferential, depicted in FIG. 2.

FIGS. 2-6B are drawn approximately to scale. However, other relativecomponent dimension may be used, in other embodiments.

DETAILED DESCRIPTION

The following description relates to a differential system for use in avehicle. In one example, the differential may be a limited slipdifferential that allows the deviation of speed between axle shafts tobe constrained. The differential case may have lubrication ports thatopen into targeted regions of the differential to enhance lubricantdistribution in areas of the differential assembly that experiencehigher loads. This lubrication port configuration decreases wear on thegearing system of the differential. Accordingly, the differential'slongevity is increased. Because of the inclusion of multiple lubricationports positioned about the case of the differential, more balancedlubricant distribution may be achieved. This enhanced lubricationdistribution decreases the potential for uneven component wear. Thedifferential may further include a split tooth pinion gearconfiguration. The split tooth pinion gears include asymmetricallyarranged toothed and untoothed portions. The asymmetric split meshpinion gears may allow for more balanced contact pressure between thegears and further decrease tooth wear.

FIG. 1 depicts a vehicle with a drivetrain that includes a differentialfor limiting rotational speed variance between two drive axles, and alubrication system for supplying lubricant to the differential todecrease component wear. FIG. 2 depicts a differential with sets ofsplit mesh pinion gears and lubrication ports arranged to provide a morebalanced lubricant flow pattern to reduce uneven wear amongst thecomponents to increase the differential's lifespan. FIG. 3 shows thedifferential with pairs of pinion gears that are arranged symmetricallyaround the case, which may reduce rotational imbalances within thedifferential and further reduce differential wear. FIGS. 4A and 4Billustrate different lubricant flow patterns which more efficientlydistribute lubricant to higher wear areas when the differential isstationary and rotating, respectively. FIG. 5 depicts the arrangement ofgears within the differential case, and particular higher load regionsof the gear assembly to which lubricant is routed via the lubricationports. FIGS. 6A and 6B show the pinion gears with a tooth chamfergeometry designed to further reduce gear wear.

FIG. 1 schematically illustrates a vehicle 10 with a powertrain 12according the present disclosure. The vehicle may take a variety offorms in different embodiments such as a light, medium, or heavy dutyvehicle. To generate power, the powertrain 12 may comprise a motivepower source 14. The power source may include an internal combustionengine, electric motor, combinations thereof, or other suitable devicedesigned to generate rotational energy. The internal combustion enginemay include conventional components such as cylinder(s), piston(s),valves, a fuel delivery system, an intake system, an exhaust system,etc. Further, the electric motor may include conventional componentssuch as a rotor, a stator, a housing, and the like for generatingmechanical power as well as electrical power during a regeneration mode,in some cases. As such, the powertrain may be utilized in a hybrid orelectric vehicle (e.g., battery electric vehicle). Therefore, thepowertrain may have a parallel, a series, or a series-parallel hybridconfiguration, in certain instances. In other examples, however, thevehicle may solely use an internal combustion engine for powergeneration.

The motive power source 14 may provide mechanical power to thedifferential 18 via a transmission 16. The power path may continuethrough the differential 18 to drive wheels 24, 26 by way of axle shafts20, 22, respectively. As such, the differential 18 distributesrotational driving force, received from transmission 16, to the drivewheels 24, 26 of axle shafts 20, 22, respectively, during certainoperating conditions.

The transmission 16 has a gear reduction that provides a speed-torqueconversion functionality. To elaborate, the transmission 16 may be ashiftable gearbox, a continuously variable transmission, an infinitelyvariable transmission, and the like. The transmission may make use ofmechanical components such as shafts, gears, bearings and the like toaccomplish the aforementioned gear reduction functionality.

The differential 18 is designed to permit speed deviation between theaxle shafts during certain conditions, such as cornering. However, toincrease vehicle traction, the differential may be a limited slipdifferential designed to constrain speed deviation between the axleshafts 20, 22, during certain conditions. In particular, when thevehicle is operating in a low traction environment, the drive wheels mayexperience differing friction coefficients. In these environments, therotational speed of the left and right drive wheels may vary dependingon the friction coefficient. As this speed difference increases, thelimited slip differential may increase friction between the pinion gearsthat mesh with the slipping side gear and the pinion pockets to limitthe speed deviation between the drive wheels. Hence, vehicle handlingperformance may be enhanced when a limited slip differential isutilized. To accomplish this speed constraint functionality, thedifferential may include a case, sets of pinion gears, and side gearsdescribed in greater detail herein with regard to FIGS. 2-6B.

FIG. 1 further shows a lubrication system 28 designed to supplylubricant (e.g., natural and/or synthetic oil) to components of thetransmission 16. In one example, to carry out the lubricantdistribution, the lubrication system 28 includes a reservoir 30 (e.g., asump), a pump 32 for driving lubricant flow through the system, aplurality of conduit 34, and/or other suitable lubricant distributioncomponents such as nozzles, valves, jets, and the like. The conduits, inthe illustrated example, are routed from the pump 32 to the transmission16, and from the transmission to the reservoir 30. Additionally, thedifferential 18 may include an enclosed splash lubrication arrangement.In such an example, as the differential rotates, lubricant may be pickedup and distributed to various components of the differential from a sump33 in the differential. As such, the lubricant in the differential maybe self-contained and may not be in fluidic communication with thelubricant conduits in the transmission, in one example. However, inother examples, lubricant may be routed between the transmission and thedifferential and from the differential to the reservoir. Other lubricantrouting schemes have been contemplated, such as conduit arrangementsthat flow lubricant in parallel through the transmission and thedifferential.

The vehicle 10 may include a control system 40 with a controller 42. Thecontroller may include a processor 44 and a memory 46 holdinginstructions stored therein that when executed by the processor causethe controller to perform various methods, control techniques, etc.described herein. The processor may include a microprocessor unit and/orother types of circuits. The memory may include known data and storagemediums such as random access memory, read only memory, keep alivememory, combinations thereof, etc. The memory may further includenon-transitory memory.

The control system 40 may receive various signals from sensors 48positioned in different locations in the vehicle 10 and the powertrain12. Conversely, the controller may send control signals to variousactuators 50 coupled at different locations in the vehicle andpowertrain. For example, the controller may send signals to the motivepower source 14. Responsive to receiving the command signal, an actuatorin the motive power source may adjust output speed or torque. Othercontrollable components in the vehicle and transmission system mayfunction in a similar manner with regard to receiving command signalsand actuator adjustment. For instance, the pump 32 may receive controlsignals which trigger adjustment of a pump actuator to vary the pump'soutput flowrate. Further, during a drive mode, the controller may adjustthe motive power source to achieve a desired vehicle speed, forinstance. Conversely, during a coast mode, the power source may beinactive and power may travel from the wheel to the differential and soforth.

An axis system 170 is provided in FIG. 1 as well as FIG. 2-6B, forreference. The z-axis may be a vertical axis (e.g., parallel to agravitational axis), the x-axis may be a lateral axis (e.g., horizontalaxis), and/or the y-axis may be a longitudinal axis, in one example.However, the axes may have other orientations, in other examples. Acentral axis 172 of the differential system is further provided in FIG.2-5, for reference. It will be understood that the central axis 172 maybe the rotational axis of the side gears and axle shafts in thedifferential system. As described herein, axial movement may refer to acomponent's movement along a direction parallel to the central axis.

FIGS. 2-3 show a differential 100. The differential 100 represents anexample of the differential 18, shown in FIG. 1. As such, thesedifferentials may share common structural and functional features. FIG.2 specifically illustrates an exploded view of the differential 100while FIG. 3 illustrates an assembled view of the differential 100. Eachof the pinion gears in the first set of pinion gears 106 has an axis ofrotation 176 and each of the pinion gears in the second set of piniongears 108 has an axis of rotation 178. The rotational axes 176 and 178,as well as central axis 172 of the differential, are shown to beparallel when the differential is assembled. However, during certainconditions the rotational axes of the pinion gears may not be parallelto the central axis.

Turning specifically to FIG. 2, the differential 100 comprises a case102 that houses a gear assembly 104. The gear assembly comprises a firstset of pinion gears 106 and a second set of pinion gears 108. Each ofthe first and second sets of pinion gears 106, 108, includes a pluralityof pinion gears 109, 111, respectively. The first and second sets ofpinion gears 106, 108 may include an even number of gears to reducerotational imbalances and differential wear. However, the sets of piniongears may include an odd number of gears, in other embodiments, whichmay increase rotational imbalances.

The pinion gears in each of the sets 106, 108 may have asymmetricallyarranged toothed and untoothed sections. Specifically, in one example,each pinion gear in the gear sets may have a similar size and toothpattern as the pinion gears in the first set. Further, the gears in eachset have an opposite arrangement with regard to the axial ends of thegears. In this way, each set of pinion gears has a common split toothedarrangement but are oppositely oriented to mesh with different sidegears 126, 128. Such an arrangement, having asymmetrically toothed firstand second sets of meshing pinion gears, may provide more even contactpressure. As a result, tooth wear is decreased and differentiallongevity is increased.

Each of the pinion gears 109 in the first set of pinion gears 106therefore includes an untoothed section 110 positioned between a widertoothed section 112 and a narrower toothed section 114. As such, thegears may have a wider toothed section and a narrowed toothed section onopposing axial sides. Likewise, each of the pinion gears 111 of thesecond set of pinion gears 108 includes an untoothed section 116positioned between a wider toothed section 118 and a narrower toothedsection 120. Further, the untoothed sections of the gears have a smallerdiameter than the outer diameter of the toothed sections, to avoidundesired interaction between the pinion gears and the side gears.

Each pair of adjacent gears 109, 111 are arranged so that the narrowertoothed sections 114, 120 mesh with the wider toothed sections 112, 118of the opposing gear, which may more evenly balance contact pressure.Further, the untoothed sections 110, 116 of the first set of piniongears axially span the second side gear, and the second untoothedsections of the second set of pinion gears axially span the first sidegear. In this way, undesired interaction between the first set of piniongears and the second side gear as well as the second pinion gear set andthe first side gear can be avoided.

The pinion gears of the first and second sets of pinion gears 106, 108may be arranged in an alternating pattern in corresponding recesses 122(e.g., pockets) of the case. To elaborate, the recesses 122 may beshaped to house pairs of pinion gears formed between the first andsecond pinion gear sets. As such, the recesses may have adjacentpartially cylindrical faces 124 sized to receive these gear pairs.Specifically, in each gear pair, the narrower toothed sections mesh withthe wider toothed sections, when assembled.

The gear assembly 104 further includes the first side gear 126 thatmeshes with the wider toothed sections 112 of the gears in the firstpinion gear set 106. Likewise, the second side gear 128 in the gearassembly 104 meshes with the wider toothed sections 118 of the secondpinion gear set 108. As illustrated, the first and second side gears126, 128 include exterior untoothed sections 130, 132 arranged outboardfrom exterior toothed sections 134, 136, respectively. The untoothedsections of the side gears may allow the side gears' structuralintegrity to be increased. Further, the untoothed side gear sections mayfacilitate a stronger attachment between the side gears and axle shaftsby extending the axial lengths of the splines, if desired. However, inalternate examples, the side gears may not include the untoothedsections.

The side gears 126, 128 may further include interior splines 138, 140profiled to mate with axle shafts which may increase assembly efficiencyduring manufacturing and repair. However, additional or alternateattachment techniques may be used to couple the axle shafts to the sidegears such as bolts, welds, press fitting, and the like.

The untoothed sections 130, 132 of the side gears may extend to outboardaxial sides 141, 143 of the gears. Conversely, the toothed sections 134,136 may extend to inboard sides 145, 147 of the side gears. The inboardsides 145, 147 have contact surfaces 149, 151, respectively, which maybe perpendicular to the central axis 172, whose surface area isincreased (e.g., maximized) to allow the gear withstand greater loading.The differential's applicability may consequently be expanded across awider range of vehicle platforms, if desired.

The differential 100 may generate a limiting force to constrain therelative rotational speed of the side gears 126, 128 via frictionexhibited between the pinion gears and the case. To expound, the firstand second sets of pinion gears 106, 108 and the first and second sidegears 126, 128 may be formed as generally cylindrical helical gears. Assuch, the meshing forces between the first set of pinion gears 106 andthe first side gear 126, and between the second set of pinion gears 108and the second side gear 128, generate meshing reaction forces in axialand radial directions in both drive and coast/reverse modes ofoperation. The axial force components generate a frictional forcebetween end surfaces 160 of the pinion gears 109, 111 and thedifferential case 102. Likewise, the radial force components generate africtional force between the tooth surfaces 162 of the pinion gears 109,111 and the pinion pockets in the differential case, thereby limitingaxle shaft speed variance permitted by the differential 100. In otherwords, the differential may transfer more torque to the side gear whoseassociated drive wheel has less traction.

During drive operation, the mechanical power path may travel fromupstream components to the differential case 102, via an input gear(e.g., ring gear). Next, the case transfers power to each set of piniongears 106, 108. The first set of pinion gears 106 then transfers powerto the first side gear 126 and the second set of pinion gears 108transfers power to the second side gear 128. From the side gears, powermay travel through associated axle shafts to the drive wheels.Conversely, during coast operation, the power path is reversed.

Further, during drive operation, the axial thrust load on the secondside gear 128 may be in an inboard direction 142. In this regard,inboard refers to a direction extending toward a center (e.g., radiallyoriented central plane) of the differential and outboard converselyindicates a direction extending away from the center. Specifically, thiscentral plane may radially extend between contact surfaces 149, 151. Insome cases, a cover may be attached via fasteners to the differentialcase 102 to enclose the gear assembly 104. When the differential isdesigned with an inboard load on the side gear, undesired loading offasteners that attach a cover, discussed in greater detail herein withregard to FIG. 3, to the case 102 may be reduced. Correspondingly, theaxial loads on the second set of pinion gears 108 may be in directionsthat extend outboard away from the wider toothed sections 116, asindicated by arrow 144.

FIG. 3 shows an assembled view of the differential 100 with the gearassembly 104 at least partially enclosed in the case 102. In oneexample, the case 102 may have a continuous (e.g., monolithic)structure. By forming the case in this manner, the overall strength andreliability of the differential may be enhanced due to the eliminationof fasteners that are used to connect multiple case components (e.g.,two case halves). Further, designing the differential assembly with amonolithic case may allow for a reduction in the overall number ofparts, a reduction in assembly time, and/or the simplification of partmanufacture to be realized. The case 102 may include a surface hardenedmaterial. For instance, the case may be constructed out of a carburizedmaterial, such as steel. Carburizing is a treatment process where metalis heated with charcoal, carbon monoxide, or another suitable carbonsource. In other instances, the case may be hardened via a nitridingprocess, diffusing nitrogen into the surface of a metal case, or aferritic nitrocarburizing process, diffusing nitrogen and carbon intothe surface. In one specific example, the metal case may be carburizedto attain a hardness that is greater than or equal to 80 Rockwellhardness measured on the A scale (HRA). Hardening of the case in thismanner allows the case to resist surface degradation (e.g., abrasion)more effectively, thereby enhancing wear resistance and increasing thelongevity of the case and differential as a whole.

The first and second sets of pinion gears 106, 108 are again illustratedin FIG. 3. Specifically, the pairs of gears formed between gears in thedifferent pinion gear sets and positioned within the recesses 122 in thecase 102 are shown. The recesses 122 of case 102 may have a relativelysmooth surface. For instance, the surface finish of the pinion pocketsmay be less than or equal to 60 microns (μm). Providing internalrecesses 122 within this surface finish range reduces surface friction.In particular, when lubricant is introduced into the interior of case102 of the differential 100, and thus into recesses 122, the surfacefinish of the recesses may reduce the likelihood of excessive reductionof the viscosity of the lubricant. Hence, undesirable increases infriction and wear within the case 102 may be avoided to further increasethe longevity of the differential 100. However, the surface finish ofthe case may be greater than 60 μm, which may, however, increase surfaceabrasion.

The recesses 122 and gears housed therein, correspondingly, may besymmetrically arranged within the case 102 with regard to the centralaxis 172. Because of the symmetric gear arrangement, more balanced loaddistribution in the differential may be achieved. Nonetheless,asymmetric gear arrangements have been envisioned.

It will be understood that a case cover and an input gear (e.g., ringgear) may be coupled to the case 102. Further, the differential may beenclosed in a housing containing lubricant, such that rotation of thedifferential by the input gear may splash lubricant within the housing.The case may include ports to enable the flow of lubricant in thehousing to be directed to and from the case to lubricate various gearcomponents contained therein, as described herein with reference toFIGS. 4A-4B. The cover may be attached to a first side 203 (e.g., leftside in the frame of reference of FIGS. 2-3) of the case 102 opposite toa second side 205 (e.g., right side in the frame of reference of FIGS.2-3) which may include the axle shaft sleeve 204. The cover allows forfurther enclosure of the pinions. The input gear 200, which isschematically depicted in FIG. 3, may be directly attached to anextension 202 in the case 102. As illustrated, the extension 202 ispositioned on the first side 203 of the case, although other positionshave been contemplated.

The interfaces 146 where the narrower toothed sections 114 of the piniongears 109 in the first set mesh with the wider toothed sections 118 ofthe pinion gears 111 in the second set are further shown in FIG. 3.Thus, the first and second sets of pinion gears 106, 108 form multiplepairs of meshing pinion gears. Further, the interfaces 146 between thenarrower toothed sections of the pinion gears 109 and the wider toothedsections 118 of the pinion gears 111 may be positioned radially outwardfrom the untoothed section of the side gear 128. This gear layout avoidsundesired interaction between the pinion and side gears. Further,positioning the pinion gears in this manner enables the diameter of theaxle shafts to be increased, if wanted, when compared to differentialdesigns which have pinion gears radially overlapping the side gears.

The case 102 may further comprise a plurality of lubrication ports 150,shown in FIGS. 2 and 3, that opens radially adjacent to one of thepinion gears in the first set of pinion gears 106. In one example, thelubrication ports 150 each open radially adjacent to a separate one ofthe pinion gears 109 in the first pinion gear set. In particular, thelubrication ports may open adjacent to portions of the untoothedsections 110 of pinion gears in the first set of pinion gears 106. Insome examples, the case 102 may not include lubrication ports adjacentto the second untoothed sections of the pinion gears in the second setof pinion gears. In this manner, lubricant may be distributed toselected regions of the differential assembly that experience higherloads, during certain conditions. As a result, component wear isdecreased and differential longevity is increased. Further, such aconfiguration may provide more balanced lubricant distribution withinthe case of the differential, thereby decreasing the potential foruneven component wear.

FIGS. 4A and 4B provide cross-sectional views of the differential 100 ofFIG. 3. Each cross-sectional view, as shown in FIGS. 4A and 4B, isdefined by a lateral cut taken along a dashed line 4-4 of the assembleddifferential 100 of FIG. 3. The lateral cut plane may pass through thefirst set of pinion gears 106, the side gears 126, 128, and twolubrication ports of the plurality of lubrication ports 150, such thatthe lateral cut divides the differential 100 into two equal parts. FIGS.4A and 4B are described herein collectively.

The cross-sectional views of FIGS. 4A and 4B illustrate the differentialcase 102, the first set of pinion gears 106, and the side gears 126,128. The second set of pinion gears 108, shown in FIGS. 2-3, areobscured from view in FIGS. 4A and 4B. However, as indicated above, thefirst and second sets of pinion gears mesh with one another and thefirst and second side gears 126, 128 respectively.

Pairs of pinion gears, from the first and second sets are arranged inthe recesses 122 (e.g., pinion pockets) throughout differential case102. Specifically, as shown in FIGS. 4A-B, the first set of pinion gears106 are oriented so that the wider toothed portions 112 are located atthe right side of the case, so as to mesh with the exterior toothedsection 134 of the first side gear 126.

Further, the untoothed sections 110 of the gears 109 in the first setmay have a length sufficient to axially span the exterior toothedsection 136 of the second side gear 128. The narrower toothed sections114 of the first set of pinion gears, located opposite the wider toothedsections 112, may be positioned adjacent the exterior untoothed section132 of the second side gear 128.

Similarly, the second set of pinion gears are oriented so that thesecond wider toothed sections are positioned at the left side of thecase 102, so as to mesh with the exterior toothed section 136 of thesecond side gear 128. Further, the untoothed sections of the second setof pinion gears may have a length sufficient to axially span theexterior toothed section 134 of the first side gear 126. Still further,the narrower toothed sections of the second set of pinion gears may bepositioned adjacent the exterior untoothed section 130 of the first sidegear 126, so that the second set of pinion gears 108 and the first sidegear 126 do not directly interact. This orientation of the first andsecond sets of pinion gears, allows meshing of each pair of pinion gearsarranged within case 102. Specifically, the wider toothed sections 112of the gears 109 mesh with the narrower toothed sections of the secondset of pinion gears. Conversely, narrower toothed sections 114 of thegears 109 mesh with the wider toothed sections of the second set ofpinion gears.

FIGS. 4A and 4B illustrate the flow of lubricant through a case of adifferential according to the present disclosure. In the lubricationsystem arrangement shown in FIGS. 4A and 4B, a first lubrication port152 is located at an upper side of the case and a second lubricationport 154 located at a lower side of the case. Further, the lubricationports 150 each open radially adjacent the untoothed section 110 of aseparate pinion gear in the first set of pinion gears 106. Accordingly,the lubrication ports may be symmetrically arranged around thedifferential case 102 in relation to planes that extend through thecentral axis 172, in order to distribute lubricant in a more effectivemanner. Likewise, the first set of pinion gears 106 may be symmetricallyarranged within case 102. However, other arrangements of lubricationports have been envisioned.

When the differential case 102 is stationary, as shown in FIG. 4A,lubricant may flow downwardly, due to gravity, through the case. Assuch, the lubricant in the case may not be pressurized via pumps orother lubrication system components. Hence, while the case isstationary, lubricant may enter the case 102 through the upperlubrication port 152, as indicated by arrow 400. The lubricant thenflows downwardly into the case 102. In the case, lubricant isdistributed from the untoothed sections 110 of the gears 109 to thewider toothed portions of the gears in the second set. Next, lubricantmay flow around the second side gear 128 and the interfaces formedbetween the gears in the second set and the second side gear. Finally,lubricant travels through a lower pair of recesses and out of the lowerlubrication port 154, indicated via arrow 402. In this manner, lubricantmay be distributed to a significant portion of the gearing system of thedifferential.

When the differential case 102 is rotating, as shown in FIG. 4B,centrifugal forces cause lubrication to flow out of the differentialcase 102 through the plurality of lubrication ports 150, as indicated byarrows 404, 406. In other words, as the case rotates, the lubricantflows radially outward through each of the plurality of lubricationports 150. Specifically, as differential case 102 rotates, the pairs ofpinion gears 106, 108 in corresponding recesses 122 also revolve withthe case, and lubricant may be routed throughout the interior of case102 as it exits the case. In this way, lubricant is provided to theinterfaces between gears 109, 111 and first and second side gears 126,128, respectively, as well as the interior surfaces of case 102.

FIG. 5 shows another cross-sectional view of the differential 100. Thecross-sectional view, as shown in FIG. 5, is defined by an axial cuttaken along a dashed line 5-5 of the differential 100 of FIG. 3, inorder to show an interior of the assembled differential. The axial cutplane may pass through the plurality of lubrication ports 150, thesecond side gear 128, and the first and second sets of pinion gears 106,108.

FIG. 5 illustrates the differential case 102, the first and second setsof pinion gears 106, 108, the second side gear 128, and the plurality oflubrication ports 150. The lubrication ports 150 in the case 102 openadjacent the untoothed section 110 of a pinion gear in the first set ofpinion gears 106. Each lubrication port may be radially aligned andpositioned outward from an untoothed section of one of the pinion gears109. As such, each lubrication port may extend from an exterior surface500 of the case to an interior surface 502 that forms a portion of apinion pocket that houses the associated pinion. However, asillustrated, the pinion pocket of the adjacent gear in the second setdoes not include a lubrication port. Put another way, the pockets forthe pinion gears in the second set may have an uninterruptedcircumferential surface. In this way, lubricant may be strategicallydirected to the untoothed sections of the gears in the first set toenhance lubricant distribution. Alternatively, the case may includeports adjacent to the gears in the second set, which may howeverincrease lubricant flow imbalances and decrease the case's structuralintegrity.

To reduce flow restriction, each lubrication port of the plurality oflubrication ports 150 may, in one example, have a diameter 504 that issubstantially constant along the length (e.g., axial length) of theport. However, in an alternate example, the diameter of each lubricationport may taper along the axial length of the port to provide a moretargeted lubrication flow through each port. Further, in certaininstances, the diameter 504 of each lubrication port may be greater thana diameter 506 of the untoothed section 110, to increase lubricationflow around the gears 109. However, lubrication ports with otherprofiles may be used in other examples, which may alter the lubricantdistribution pattern.

The plurality of lubrication ports 150 may be conceptually divided intotwo pairs that are positioned on opposing sides of the case 102.Arranging the ports in this manner allows at least one of the ports toremain in an upper quadrant and one to remain in a lower quadrant whenthe case is stationary. Consequently, the rotational position of thecase may not impede the gravity driven lubrication flow through thecase. In other examples, the case may include only one pair oflubrication ports, which may impact flow dynamics, or more than twopairs of ports which may decrease the case's structural integrity, forinstance.

FIG. 5 further illustrates the meshing of the second side gear 128 withthe second set of pinion gears 108. More particularly, the teeth of thesecond side gear mesh with the wider toothed portions 118 of gears 111.In this assembled configuration, the teeth of the second side gear 128are positioned adjacent the untoothed sections 110 of the gears 109.Accordingly, the untoothed sections 110 of the gears 109 may axiallyspan the second side gear 128.

FIGS. 6A and 6B show detailed views of chamfered edges of toothedsections of an example pinion gear 600 in the first set of pinion gears106, depicted in FIGS. 1-5. Since the pinion gears in both of the firstand second sets of pinion gears may have a similar size and geometry,the gear tooth geometry illustrated in FIGS. 6A and 6B may be applicableto either of the first and second sets of pinion gears.

FIG. 6A illustrates the narrower toothed section 114 of the examplepinion gear 600 with a plurality of teeth. The narrower toothed section114 of the pinion gear 600 includes an end face 601. When assembled inthe differential, the end face 601 is adjacent to the wider toothedsections of the gears in the second set. Each tooth of the pinion gear600 includes a drive side (e.g., convex flank) 604 and a coast side(e.g., concave flank) 606 joined by a top land 608.

Each tooth in the pinion gear 600 may additionally include a chamfer 610between the drive side 604 and the top land 608. The chamfer 610 mayhave a width 611, which may be between 0.45 millimeters (mm) and 0.25mm. In other examples, the width 611 of chamfer 610 may be outside ofsuch a range (e.g., having a width of greater than 0.45 mm or less than0.25 mm). The tooth may further include a chamfer 612 between the topland 608 and the coast side 606. The chamfer 612 may have an angle 613,as indicated in FIG. 6A, which may be between 15° and 20°. Thus, theangle may therefore be measured between planar surfaces of the top landand the chamfer that intersect one another. Designing teeth which arechamfered in this range may decrease gear wear which further increasesthe differential's lifespan. In other examples, the angle 613 of thechamfer 612 may be outside the aforementioned range (e.g., greater than20° or less than 15°).

FIG. 6B illustrates the narrower toothed section 114 of the pinion gear600 with teeth that have the drive side 604, coast side 606, and topland 608. An end face 602 of the pinion gear 600 is shown in FIG. 6B.With reference to FIG. 2, the end face 602 may be a left end face.

Turning back to FIG. 6B, the pinion gear 600 includes a chamfer 620between the end face 602 and the drive side 604. The chamfer 620 has awidth 622 and a length 624. The width 622 of chamfer 620 may be between0.70 mm and 0.30 mm, in one example. Further, in certain instances, thelength 624 of chamfer 620 may be between 0.80 mm and 0.40 mm. A chamfer620 designed within the aforementioned ranges may be small enough toprovide a larger contact area between top land 608 and a correspondingpinion pocket, when the pinion gears are assembled within the case.Further, the chamfer 620 may be sized to reduce the chance of thechamfer diminishing or reducing through the lifespan of the pinion gear.An angle measured between planar surfaces of the top land 608 and thechamfer 620, as determined by the width 622 and length 624, may be assmall as possible while still allowing for the accumulation of debrisand/or burrs from surface wear, in one example. In this way, excessivefriction due to buildup of debris between the pinion gears and pinionpockets is avoid, thereby reducing wear on the gearing system. However,in other examples, chamfer 620 may have a different angle, length,and/or width outside of the aforementioned ranges.

FIGS. 1-6B show example configurations with relative positioning of thevarious components. If shown directly contacting each other, or directlycoupled, then such elements may be referred to as directly contacting ordirectly coupled, respectively, at least in one example. Similarly,elements shown contiguous or adjacent to one another may be contiguousor adjacent to each other, respectively, at least in one example. As anexample, components laying in face-sharing contact with each other maybe referred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example. Asyet another example, elements shown above/below one another, at oppositesides to one another, or to the left/right of one another may bereferred to as such, relative to one another. Further, as shown in thefigures, a topmost element or point of element may be referred to as a“top” of the component and a bottommost element or point of the elementmay be referred to as a “bottom” of the component, in at least oneexample. As used herein, top/bottom, upper/lower, above/below, may berelative to a vertical axis of the figures and used to describepositioning of elements of the figures relative to one another. As such,elements shown above other elements are positioned vertically above theother elements, in one example. As yet another example, shapes of theelements depicted within the figures may be referred to as having thoseshapes (e.g., such as being circular, straight, planar, curved, rounded,chamfered, angled, or the like). Additionally, elements co-axial withone another may be referred to as such, in one example. Further,elements shown intersecting one another may be referred to asintersecting elements or intersecting one another, in at least oneexample. Further still, an element shown within another element or shownoutside of another element may be referred as such, in one example. Inother examples, elements offset from one another may be referred to assuch.

The invention will be further described in the following paragraphs. Inone aspect, a differential is provided that comprises a first set ofpinion gears with each gear including a first untoothed sectionpositioned between a first wider toothed section and a first narrowertoothed section; a first side gear meshing with the first wider toothedsections; a second set of pinion gears with each gear including a seconduntoothed section positioned between a second wider toothed section anda second narrower toothed section; a second side gear meshing with thesecond wider toothed sections; a case at least partially enclosing thefirst and second sets of pinion gears and including a lubrication portthat opens radially adjacent to one of the pinion gears in the first setof pinion gears; wherein, during a drive state, an axial load on thesecond side gear is in an inboard direction.

In another aspect, a limited slip differential is provided thatcomprises a first set of pinion gears with asymmetrically arrangedtoothed and untoothed sections; a second set of pinion gears withasymmetrically arranged toothed and untoothed sections, wherein aportion of the toothed sections in the first and second set of piniongears mesh with each other; a first side gear meshing with a portion ofthe toothed sections in the first set of pinion gears; a second sidegear meshing with a portion of the toothed sections in the second set ofpinion gears; and a monolithic case at least partially enclosing thefirst and second sets of pinion gears and including a plurality oflubrication ports that each open radially adjacent to the untoothedsections of the first set of pinion gears; wherein, during a drivestate, an axial load on the second side gear is in an inboard directionand axial loads on the second set of pinion gears are in directionsextending outboard away from the second narrowed toothed sections.

In any of the aspects or combinations of the aspects, the lubricationport may be included in a plurality of lubrication ports in the case andwherein each lubrication port in the plurality of lubrication ports mayopen adjacent to a separate pinion gear included in the first set ofpinion gears.

In any of the aspects or combinations of the aspects, the case may notinclude lubrication ports adjacent to the second untoothed sections ofthe pinion gears in the second set of pinion gears.

In any of the aspects or combinations of the aspects, the plurality oflubrication ports may open adjacent to the untoothed sections of thepinion gears in the first set of pinion gears.

In any of the aspects or combinations of the aspects, each lubricationport of the plurality of lubrication ports opens adjacent to the firstuntoothed section of the respective pinion gear in the first set ofpinion gears.

In any of the aspects or combinations of the aspects, during the drivestate, axial loads on the first set of pinion gears may be in directionsthat extend outboard away from the first wider toothed sections.

In any of the aspects or combinations of the aspects, during astationary state, lubricant may flow inward through an upper lubricationport in the plurality of lubrication ports and outward through a lowerlubrication port in the plurality of lubrication ports.

In any of the aspects or combinations of the aspects, during driveoperation, lubricant may flow radially outward through the plurality oflubrication ports.

In any of the aspects or combinations of the aspects, the first narrowertoothed sections may mesh with the second wider toothed sections; andthe second narrower toothed sections may mesh with the first widertoothed sections.

In any of the aspects or combinations of the aspects, the case may forma continuous structure.

In any of the aspects or combinations of the aspects, the first andsecond narrower toothed sections may be chamfered, wherein an angle ofthe chamfer is between 15° and 20°.

In any of the aspects or combinations of the aspects, the case may becarburized.

In any of the aspects or combinations of the aspects, the first narrowertoothed sections may include an outer axial side that is chamfered.

In any of the aspects or combinations of the aspects, during the drivestate, axial loads on the second set of pinion gears may be indirections that extend outboard away from the second narrower toothedsections; and the first narrower toothed sections of the first set ofpinion gears through which lubricant flow are arranged adjacent to thesecond wider toothed sections of the second set of pinion gears.

In any of the aspects or combinations of the aspects, the first narrowertoothed sections may include chamfers on axial ends of the teeth.

In any of the aspects or combinations of the aspects, during astationary state, lubricant flow through the plurality of lubricationports may be gravity driven.

In any of the aspects or combinations of the aspects, during a drivestate, lubricant flow through the plurality of lubrication ports may becentrifugally driven.

In any of the aspects or combinations of the aspects, the plurality oflubrication ports may include two lubrication ports positioned onopposing sides of the case.

In any of the aspects or combinations of the aspects, the untoothedsections in the first set of pinion gears may axially span the secondside gear and the untoothed sections in the second set of pinion gearsmay axially span the first side gear.

In any of the aspects or combinations of the aspects, an axial load onthe first side gear may be in an inboard direction and axial loads onthe first set of pinion gears may be in directions extending outboardaway from the first wider toothed sections.

In any of the aspects or combinations of the aspects, internal recessesin the case that enclose the first and second sets of pinion gears mayhave a surface finish less than or equal to 60 microns (μm).

In any of the aspects or combinations of the aspects, the case may becarburized and has a hardness that is greater than or equal to 80Rockwell hardness on the A scale (HRA).

In any of the aspects or combinations of the aspects, wherein a width ofthe chamfer may be between 0.45 and 0.25 millimeters (mm).

In any of the aspects or combinations of the aspects, a width of thechamfer of the first narrower toothed sections may be between 0.70millimeters (mm) and 0.30 mm and a length of the chamfer of the firstnarrower toothed sections may be between 0.80 mm and 0.40 mm.

In another representation, a limited slip differential is provided thatcomprises: two sets of asymmetric split pinion gears that mesh with oneanother and corresponding side gears; and a plurality of openlubrication holes that are arranged symmetrically with regard toradially alignment and adjacent the untoothed portion of only one of thesets of gears.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevant artsthat the disclosed subject matter may be embodied in other specificforms without departing from the spirit of the subject matter. Theembodiments described above are therefore to be considered in allrespects as illustrative, not restrictive.

As used herein, the term “approximately” and “substantially” areconstrued to mean plus or minus five percent of the range unlessotherwise specified.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to avariety of vehicles such as vehicles with hybrid electric powertrains,combustion engine powertrains, electric powertrains, and the like.Moreover, unless explicitly stated to the contrary, the terms “first,”“second,” “third,” and the like are not intended to denote any order,position, quantity, or importance, but rather are used merely as labelsto distinguish one element from another. The subject matter of thepresent disclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A differential, comprising: a first set ofpinion gears with each gear including a first untoothed sectionpositioned between a first wider toothed section and a first narrowertoothed section; a first side gear meshing with the first wider toothedsections; a second set of pinion gears with each gear including a seconduntoothed section positioned between a second wider toothed section anda second narrower toothed section; a second side gear meshing with thesecond wider toothed sections; and a case at least partially enclosingthe first and second sets of pinion gears and including a lubricationport that opens radially adjacent to one of the pinion gears in thefirst set of pinion gears; wherein, during a drive state, an axial loadon the second side gear is in an inboard direction.
 2. The differentialof claim 1, wherein the lubrication port is included in a plurality oflubrication ports in the case and wherein each lubrication port in theplurality of lubrication ports opens adjacent to a separate pinion gearincluded in the first set of pinion gears.
 3. The differential of claim2, wherein the case does not include lubrication ports adjacent to thesecond untoothed sections of the pinion gears in the second set ofpinion gears.
 4. The differential of claim 3, wherein each lubricationport of the plurality of lubrication ports opens adjacent to the firstuntoothed section of the respective pinion gear in the first set ofpinion gears.
 5. The differential of claim 4, wherein, during the drivestate, axial loads on the first set of pinion gears are in directionsthat extend outboard away from the first wider toothed sections.
 6. Thedifferential of claim 2, wherein, during a stationary state, lubricantflows inward through an upper lubrication port of the plurality oflubrication ports and outward through a lower lubrication port of theplurality of lubrication ports.
 7. The differential of claim 2, wherein,during drive operation, lubricant radially flows outward through theplurality of lubrication ports.
 8. The differential of claim 1, wherein:the first narrower toothed sections mesh with the second wider toothedsections; and the second narrower toothed sections mesh with the firstwider toothed sections.
 9. The differential of claim 1, wherein the caseforms a continuous structure.
 10. The differential of claim 1, whereinthe first and second narrower toothed sections are chamfered and whereinan angle of the chamfer is between 15° and 20°.
 11. The differential ofclaim 1, wherein the case is carburized.
 12. The differential of claim1, wherein the first narrower toothed sections include chamfers on axialends of the teeth.
 13. The differential of claim 1, wherein: during thedrive state, axial loads on the second set of pinion gears are indirections that extend outboard away from the second narrower toothedsections; and the first narrower untoothed sections, around whichlubricant flows, are arranged adjacent to the second wider untoothedsections of the second set of pinion gears.
 14. A limited slipdifferential, comprising: a first set of pinion gears withasymmetrically arranged toothed and untoothed sections; a second set ofpinion gears with asymmetrically arranged toothed and untoothedsections, wherein a portion of the toothed sections in the first andsecond set of pinion gears mesh with each other; a first side gearmeshing with a portion of the toothed sections in the first set ofpinion gears; a second side gear meshing with a portion of the toothedsections in the second set of pinion gears; and a monolithic case atleast partially enclosing the first and second sets of pinion gears andincluding a plurality of lubrication ports that each open radiallyadjacent to the untoothed sections of the first set of pinion gears;wherein, during a drive state, an axial load on the second side gear isin an inboard direction and axial loads on the second set of piniongears are in directions extending outboard away from the second narrowedtoothed sections.
 15. The limited slip differential of claim 14,wherein, during a stationary state, lubricant flow through the pluralityof lubrication ports is gravity driven.
 16. The limited slipdifferential of claim 15, wherein, during the drive state, lubricantflow through the plurality of lubrication ports is centrifugally driven.17. The limited slip differential of claim 15, wherein the plurality oflubrication ports include two lubrication ports positioned on opposingsides of the case.
 18. The limited slip differential of claim 14,wherein the untoothed sections in the first set of pinion gears axiallyspan the second side gear and the untoothed sections in the second setof pinion gears axially span the first side gear.
 19. The limited slipdifferential of claim 14, wherein an axial load on the first side gearis in an inboard direction and axial loads on the first set of piniongears are in directions extending outboard away from the first widertoothed sections.
 20. The limited slip differential of claim 14,wherein: the first and second narrower toothed sections are chamfered;and an angle of the chamfer is between 15° and 20°.